Video summary

Week 01: Lecture 04: Selection of polymers in DDS

Main summary

Key takeaways

Educational

Main ideas & lessons

  • Purpose of the lecture: Introduces how to select polymers for novel drug delivery systems (NDDS).
  • Recap of prior polymer topics: Covers polymer types/classification, biodegradation, roles of polymers in drug and non-drug delivery, and the advantages/limitations of polymers.

Why polymers matter in NDDS

  • Polymers are macromolecules made of monomers.
    • They are widely used in everyday materials (e.g., packaging and food).
    • They form a foundation of the pharmaceutical industry.
  • In NDDS, combining polymer + drug + carriers/therapeutic agents/other active molecules produces “novel” delivery systems where physical state, shape, size, and surface properties can change.

Roles polymers play in drug delivery

Polymers help by:

  • Controlling drug release
    • Via mechanisms such as diffusion/dissolution
    • Also through polymer degradation and swelling
  • Protecting active molecules while traveling through the body
    • Example mechanisms include GI-related/enzymatic and pH-related degradation
  • Increasing drug loading vs conventional formulations
    • This can improve bioavailability
  • Enabling stimuli-responsive targeting
    • Using polymer classes responsive to triggers such as temperature, pH, enzymatic activity, glucose, etc.
  • Acting as stabilizers and surfactants
  • Masking bitter taste of drugs

Selection criteria for polymers (key properties)

Bulk properties

  • Affected by:
    • Molecular weight
    • Polymer adhesion
    • Solubility in the body
  • Influence release via:
    • Diffusion
    • Dissolution-controlled release
    • Physical degradation of the polymer
    • Swelling

Bioadhesiveness (mucoadhesiveness)

  • Especially important for mucosal delivery (e.g., ocular and nasal systems).
  • Mucoadhesive polymers adhere to mucus, improving:
    • Retention time
    • Contact with tissues
    • Overall drug residence/permeability

Structural properties of the matrix

  • Micromorphology and pore size affect:
    • Mass transfer of water and drugs into/out of the polymer matrix
    • The resulting release behavior

Polymer classification by responsiveness to stimuli

  • Stimuli-responsive polymers change behavior when exposed to internal or external stimuli, such as:
    • Switching between soluble and insoluble phases
    • Converting solution ↔ gel (often temperature-driven)
  • Stimuli categories:
    • Examples: temperature, light, pH, electric field, ultrasound, enzyme, oxidation, reduction
    • Internal stimuli: occur within the body
    • External stimuli: require applied external conditions/energy

Methodology / instruction-like content (detailed)

How to choose a polymer for NDDS (selection workflow implied by the lecture)

  1. Step 1: Confirm the drug delivery goal

    • Decide the required release behavior and performance, such as:
      • Controlled release
      • Targeting
      • Mucosal retention
      • Protection from degradation

  2. Step 2: Evaluate bulk properties

    • Consider:
      • Molecular weight
      • Adhesion properties
      • Solubility in the biological environment
    • Ensure the polymer supports the desired release mechanism(s), e.g.:
      • Diffusion
      • Dissolution-controlled release
      • Release via polymer physical degradation
      • Release via polymer swelling

  3. Step 3: Evaluate bioadhesiveness for mucosal routes

    • For mucosal delivery (ocular/nasal), choose polymers with appropriate mucoadhesive behavior.
    • Aim to improve permeability/retention time and contact duration with tissues.

  4. Step 4: Evaluate matrix structural properties

    • Check:
      • Micromorphology
      • Pore size
    • Goal: control water/drug mass transfer to achieve the target release profile.

  5. Step 5: Choose whether a stimuli-responsive polymer is needed

    • If you need site-specific release/activation, select a polymer responsive to the relevant trigger:
      • Temperature-responsive
      • pH-responsive
      • Glucose-responsive
      • Photoresponsive
      • Enzyme-responsive
    • Match the stimulus to what is expected at the target site.

Stimuli-responsive polymer categories covered

1) Temperature-responsive polymers

  • Core concept: The polymer undergoes a physical change with temperature, affecting phase transition and therefore targeting/release.
  • Two categories:
    • LCST (Lower Critical Solution Temperature)
      • Soluble in water at lower temperatures
      • Above LCST → becomes insoluble/precipitates
    • UCST (Upper Critical Solution Temperature)
      • Soluble at high temperatures
      • Below UCST → becomes insoluble/precipitates
  • Examples mentioned: polyacrylamide-based polymers, polyvinyl caprolactam, chitosan.

2) pH-responsive polymers

  • Core concept: Act as polyelectrolytes (weakly acidic or basic) and accept/release protons depending on pH, changing physical properties.
  • Functional groups / types mentioned:
    • carboxyl, pyridinium, sulfonic phosphate, tertiary amines
  • Examples mentioned: chitosan, polyhistidine, poly-L-glutamic acid, poly-L-aspartic acid.
  • Behavior on pH change:
    • Self-assembly into micelles
    • Swelling
    • Changes in wetting behavior
    • Possible gel formation

3) Glucose-responsive polymers (diabetes-related)

  • Core concept: Respond to glucose concentration; upon triggering, they swell and/or release drug.
  • Strategies mentioned:
    • Use glucose oxidase and phenylboronic acid (concanavalin as phrased) as a glucose response system
    • Conjugate with polymers via covalent or non-covalent conjugation
  • Example outcome: glucose stimulation leads to controlled insulin release
  • Additional example described:
    • Insulin is encapsulated/conjugated; glucose response produces a reversible complex release that triggers drug release.

4) Photoresponsive (light-sensitive) polymers

  • Core concept: Respond to UV/visible light by changing solubility, viscosity, and color.
  • Mechanism: light-sensitive groups in the polymer can produce reversible or irreversible changes under irradiation.
  • Examples mentioned:
    • azobenzene derivatives (e.g., “Aobenzene spyopiron” as transcribed)
    • coumarin-type (as phrased)
    • o-nitrobenzyl (irreversible change)
  • Application example given:
    • Photoresponsive nanocarriers for active targeting in cancer
    • Supports both:
      • diagnosis/detection
      • theranostic therapy (therapy + diagnosis)

5) Enzyme-responsive polymers

  • Core concept: Polymer structure/properties change after interaction with enzymes (in vitro/in vivo), triggering enzymatic effects.
  • Effects described:
    • Enzyme-mediated degradation
    • Formation of self-assembled structures
    • Swelling/shrinking changes
    • Drug release triggered by enzyme presence
  • Examples mentioned: chitosan and alginate, dextran, polyethylene glycol, polyethylene oxide.
  • Hydrogel example described (lysozyme-triggered):
    • Lysozyme triggers physical changes in a hydrogel → promotes degradation and drug release
  • Applications: targeting delivery and diagnostics; used to create nanocarriers/hydrogels for controlled release at target sites.

Speakers / sources featured

  • Dr. Satish Deana pelli (speaking; “Welcome back…” through “Thank you so much.”)

Original video